Don't inject until you get a steady kH measurement of 3.0°H or 3.5°H. Otherwise you could have real problems with the pH.
As to the crushed coral; it will work well, but it is slow acting and you may not see a rise in kH for a week or two. Then you can adjust the amount of coral to suit your needs. I would go with .50 cup of it and test frequently for content. IME, it's not like you're going to wake up in the morning and find a kH of 12°H. As I said it takes time to act, especially in a 90. If you find that it's not reacting as quickly as you'd like, you can also use baking soda to raise kH. Be careful with this however. It will work much more quickly to raise kH.

Start your CO2 in the morning, on a day that you will be able to monitor the pH at least every 2 hours. Start with 1 bps, and wait 2 hrs. and test for content. Adjust your needle valve in very small increments to achieve 15 - 20ppm/CO2 at lights out. NO MORE!! The following morning test again at lights on to see how the tank has reacted over night. Be conservative with the gas until you know how it will affect your water table.

With the Milwaukee controller and your setup, I'd suggest starting it at 7 until everything settles in unless this is a fishless tank. If you're trying to adjust water parameters chemically, there's going to be a bit of ripple for awhile and the fish will withstand stability in less than optimum conditions than they will wide variances. At 7, the peaks and dips will be less stressful than a baseline of 6.8, you can adjust it from there as everything settles in.

Also you'll probably want a bit more light to get some serious paybacks on the CO2 investment.

I saw you are running a pH controller and have added crushed coral to your filter Putty. I remembered reading this over at Chuck Gadd's :

Quote:

There is on case I've seen where the addition of CO2 resulted in an increase in KH. This can happen when you have something in the tank that dissolves carbonate into the water. Seashells, crushed coral, and many gravels and rocks will do this. With the addition of CO2, the water turns more acidic, which will increase the dissolving of the minerals. It appears that increasing CO2 raises the KH, which isn't really the case. The dissolving minerals raise the KH, and the increase in KH results in an increase in pH. In a system using a pH probe and controller to regulate CO2 levels, this can have fatal consequences, since the pH controller will keep trying to lower the pH, but as more CO2 is dissolved, it lowers the pH, which raises the KH, which raises the pH. So you now have more CO2, but the same pH. So the controller adds even MORE co2. And it will keep going. So it's important to know your KH whenever using pH to judge CO2 levels.

So it seems that I am stuck as to what I should do. I was hoping the 1/4 cup of crushed coral would eventually equilibriate and provide stable, higher KH (my KH is aroud 2 degrees), but that may not work.

I added some of the Hagen KH increaser to the tank last night to get it up a little bit, but am wondering if this is a good permanent solution. I know baking soda does not last long.

So what are my options? Dolomite? What product is good to increase KH and GH? My tap water is less than 1 KH and about 2 GH.

Thanks in advance.

edit - last line of that says to keep an eye on KH, so would this only occur if the KH was extremly high? I wonder how much 1/4 cup in 90gallons will actuall increase the KH over time.

I have gotten my KH up to 4. The pH at night is 7.2, and the pH in the morning is 7.2. I am running a small air pump on a timer at night.

I am going away for the weekend, but when I get back I plan to kick on the CO2 with the controller set to 7.0. This should put me at about 6.6 ppm CO2 to start. I know this is low, but I can work from there.

How huge will my CO2 loss be at night with the air pump, I am running it quite low, but is visibly helping the fish in the AM.

You should not be seeing signs of stress in your fish with a CO2 ppm of 6.6. Something is not right.
With a kH of 4°H, you should see little variance in pH over night even in the 15 - 20ppm range. If all your numbers are correct, there is something other than the gas that is stressing the fish.

You should not be seeing signs of stress in your fish with a CO2 ppm of 6.6. Something is not right.
With a kH of 4°H, you should see little variance in pH over night even in the 15 - 20ppm range. If all your numbers are correct, there is something other than the gas that is stressing the fish.

Len

I have not put the CO2 on yet. I am trying to raise KH and stabilize pH before I do.

My KH is now at 4, due to the addition of the Hagen product. I have 1/4 cup of crushed coral in the filter. pH right now is between 7.2 and 7.4 (it used to swing by .8 to .6 before I raised the KH).

I am going to turn on the CO2 on Monday and set the pH for 7.0 to start.

Will having a small pump on at night drive my CO2 consumption through the roof? I have to do this, the fish were gasping even w/o CO2. I have quite a few fish and no surface agitation.

While we talk all the time about reducing surface agitation in our planted tanks to decrease the out-gassing of CO2 you should never eliminate it. My guess upon reading this thread is that you most likely have an organic film on the surface of the water that is basically eliminating the gas exchange.

Take a look at a FISH tank. Bubble wands, HOB filters and all that stuff create a tremendous amount of surface agitation. In fact many people think the air pump is for putting air into the water. Well it does, but it does it though surface agitation more than dissolving air into the water from the bubbles.

Now look at your tank. You have NO agitation. Try getting your filter returned moved around so you do get some surface movement or get a power head. The problem of CO2 out-gassing with a pressurized system is a non-issue IMHO. I have Bio-Wheel Pro filters on my two high light planted tanks just for the fact they are very good at oxygenating the water.

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